1. Field of the Invention
The present invention relates to a reflector, an optical element, an interferometer system, a stage device, an exposure apparatus, and a device fabricating method.
2. Description of Related Art
In a process of fabricating an electronic device, such as a semiconductor device or a liquid crystal display device, a projection exposure apparatus is used that projects a pattern image of a mask or a reticle (hereinafter, generically referred to as a reticle), wherein a pattern is formed through a projection optical system onto each projection region (shot region) on a substrate (such as a wafer or a glass plate), which is coated with a photosensitive material (resist).
With such an exposure apparatus, the positional information of the stage, whereon the substrate is mounted, is measured by an interferometer system. The interferometer system irradiates a beam to a reflecting mirror (movable mirror), which is provided to the stage, and uses that reflected beam to measure the positional information of the stage (for example, refer to Published Japanese Translation No. 2001-510577 of the PCT International Publication, and the corresponding U.S. Pat. No. 6,020,964). In addition, a technology has been proposed that uses the interferometer system to measure a position (height position) of the stage in the optical axis direction of the projection optical system (for example, refer to Japanese Published Unexamined Patent Application No. 2001-345254 and the corresponding U.S. Pat. No. 6,867,849). According to this technology, it is possible to improve the speed of response and to accurately measure the position of the stage in the height direction, even if the substrate is not mounted or if the stage has moved to an area where the substrate is not present.
With a constitution wherein a reflecting plate is provided above a movable stage, it is difficult to secure a location for installing downflow equipment. In addition, if a measuring instrument, which is used to measure the position of the projection optical system and the wafer, is disposed above the movable stage in order to avoid the reflecting plate, then there is a risk that this will invite an increase in the size of the apparatus.
In addition, with a conventional interferometer system for height position measurement, the beam is bent at a prescribed angle by a reflecting mirror (movable mirror) provided to the stage, is reflected by a reflecting mirror (fixed mirror), which is fixed to a stationary object, and then returns along the original path. With such an interferometer system, the optical path length of the beam is comparatively long, and changes in the attitude of the stage therefore tend to affect the measurement result. For example, a change in the inclination of the stage results in a comparatively large positional deviation of the beam that returns from the stage and/or a comparatively large angular deviation in the return direction, and there is consequently a possibility that this will invite a detection failure and/or measurement error.